Virtualization allows multiplexing of an underlying host machine between different virtual machines. The host computer allocates a certain amount of its resources to each of the virtual machines. Each virtual machine is then able to use the allocated resources to execute applications, including operating systems (referred to as guest operating systems). The software layer providing the virtualization is commonly referred to as a hypervisor and is also known as a virtual machine monitor (VMM), a kernel-based hypervisor, or a host operating system. The hypervisor emulates the underlying hardware of the host computer, making the use of the virtual machine transparent to the guest operating system and the user of the computer.
One such resource managed by the host computer is a networking device that may be used by multiple guests operating (i.e., virtual machines) at the same time. Each guest or virtual machine is assigned a different and unique network address, such as a virtual LAN (VLAN) tag and/or a media access control (MAC) address, or some other combination of data in a packet header. The networking device has multiple queues for managing incoming packets to be received by a virtual machine and outgoing packets transmitted by a virtual machine. Dedicated queues may be used which are mapped to a specific hardware address and dedicated to a specific virtual machine. In addition, shared queues may be employed which are shared by multiple virtual machines. However, the management of the multiple dedicated and shared queues of the virtual machine system creates a significant administrative burden for the host computer administrator including the continual monitoring, evaluating and re-allocating of the queues based on the frequently changing queue activity.
When a packet is received in a shared queue, the host computer needs to look at the received packet in order to determine which guest (virtual machine) should receive the packet. As such, the packet can not be placed directly into a memory of the guest virtual machine for which it is intended. Instead, the host computer must make a copy of the packet, thereby expending additional computational and storage resources.
When a packet to be transmitted is placed in a shared queue, the host computer must examine the packet in order to validate the address. This can cause contention between multiple virtual machines seeking to utilize the same shared queue and creates a bottleneck negatively effecting network performance.
In addition, there may be a need to switch a virtual machine and its one or more associated transmit paths from one transmit queue (i.e., an old queue) to another transmit queue (i.e., a new queue). However, if the virtual machine system immediately executes the switch there may be packets that are outstanding on the old queue (i.e., the packets transmitted by the one or more virtual machine addresses affected by the switch which have been provided to a network device for transmission, but not yet transmitted). Accordingly, if the switch occurs automatically without regard to the outstanding packets on the old queue, then packets may be transmitted on the new queue before the outstanding packets are transmitted from the old queue, resulting in an out-of-sequence transmission of packets and a need to re-order the packets at the destination.